Finding The Correct Breast Pump Flange Size

Finding the right fit is always important – whether it’s for clothing, shoes, but especially when it comes to your breast pump flange size if you're a breast pumping mom. Soreness, pinching, irritation, and clogged milk ducts don’t sound fun but are all things that can occur if you don’t have the correct flange size. A breast pump flange (breast shield) size that is too small or too big could seriously hinder your pumping experience and overall breast pumping journey. So, be sure to choose the correct size to properly express milk for your infant.

A common question that many don't know is related to flange sizing is: How can we best ensure maximum milk output while pumping? The answer is making the pumping session both comfortable and efficiently stimulating the breasts. To achieve this, flange sizing is incredibly important when planning to use a breast pump. The flange mimics and simulates what a proper and comfortable latch feels and looks like from a baby’s latch. Too large, and the areola gets compressed, causing the milk to get stopped prior to release, much like a water hose kink. Too small, and the nipple receives too much friction, causing blisters, soreness, and inadequate stimulation.

It may seem overwhelming, one more thing to learn, especially for a new mom. Let’s take a closer look at the mechanics sizing to better understand and prepare for your perfect size!

First, What Is A Breast Pump Flange?

A breast pump flange is the funnel or cone-shaped plastic cup that fits directly over your nipple to form a seal around the areola to create a vacuum that gently draws the nipple into the funnel for milk extraction.

Not having the correct flange size could impact your milk flow by causing harm to the breast tissue, blocked milk ducts, pain, nipple damage, swelling, or cuts on the nipple. But with finding the right flange, you can comfortably maximize milk production.

Understanding the Fit of the Breast Pump Flange

When considering the nipple, pay close attention to how the nipple sits in the narrow tunnel of the flange. A proper fit has the nipple centered, without any rubbing on the walls. This allows the nipple to move freely and stretch.Quite similar to feeding directly: Since it's referred to as “breastfeeding” and not “nipple feeding,” the nipple is not the only part of the breast to receive attention. The narrow end of the flange should allow a subtle amount of areolar tissue at the base of the nipple. Too large a size, and the areola gets pinched or kinked, preventing the release of milk, and may even accrue blisters.The areola (uh-REE-oh-la) is the darkened area around the nipple. Lubricating pores, referred to as the Montgomery glands, are often more prominent during lactation, and are located on the areola.

The primary functions of the areola is to serve an easy-to-see bullseye for the baby to aim for when latching, but also a collective where all of the milk ducts / channels send the milk from storage.When sizing a flange, the areola should not be ignored. The funnel, or breast shield, of the flange mimics the lips of a baby. If none of the areola makes it into the mouth or the flange, there is inadequate stimulation to the breast, that may interfere with long-term supply and milk production. It may also affect comfort, as this could also mean tightness around the nipple, which has a negative impact on milk production, too.

A comfortable fit for both means less physical stress on the breasts, which helps the body relax and respond well to oxytocin, the hormone responsible for releasing milk that is produced and stored.

Finding The Correct Breast Pump Flange Size

Motif’s goal is to help mom have the most comfortable pumping journey possible. Our handy flange sizing chart helps you determine your best fit. Be sure to review each size option to choose the one that will fit best.

Flanges are sized in millimeters (mm). It should be slightly larger than the nipple measurement to allow for movement. Its also important to measure BOTH nipples, as just like in breast size, symmetry is not always part of the equation.

To determine what size you need, you’ll need to know your nipple size. You can measure your nipple by taking a ruler or measuring tape to measure the diameter of your nipple (the horizontal width across it). Measure the nipple alone, do not include the areola which is the outer edge around your nipple. The measurement should be in millimeters (1 cm = 10mm).

Then select your flange size based on your measurement.

  • If you measured up to 17mm you’ll fit in a 21mm flange.
  • If you measure up to 22mm use size 24mm.
  • If you measured up to 23mm select size 27mm.
  • If you measured up to 26mm use 30mm.
  • If you measured up to 32 mm use size 36 mm.

A quick trick for a starting place is to make the ASL sign for “I love you,” and compare the fingers for approximate nipple size comparison. The thumb 24-26 mm, the index 21-23mm, and the pinky 20 or smaller. Sizes needed would be 30, 27, and 24, respectively.

Once a size estimate is completed, gently pumping and observing the fit and movement will ensure the correct fit has been accomplished.

You’ll know if you have the right pump shield if:

  • Your nipple is in the center of the flange and moves freely into the tunnel of the breast pump for comfortable milk expression.
  • Your areola has little to no tissues inside the tunnel of the breast pump.
  • You do not feel areas of the breast that still contain milk, as this could indicate uneven breast milk extraction.
  • You don’t experience any nipple pain.
  • Your nipple and areola do not turn white or become discolored, meaning the blood supply has not been cut off.

Ashley Georgakopoulos, Motif Medical Lactation Director (IBCLC), explained that when looking for the correct fit to, “Find what is comfortable. Too much friction to the tissue, tightness, or painful sucking could indicate the incorrect size. The top of the nipple and its base should be the only part entering the flange tunnel.”

How To Tell If Your Flange Is Too Small

If your breast pump flange is too small you may experience:

  • Rubbing as the nipple is pulled against the sides of the breast pump tunnel.
  • Pinching and squeezing of the nipple.
  • Your nipple or areola becomes white or discolored.
  • Low breast milk production.Painful milk extraction.

How To Tell If Your Flange Is Too Big

If your breast pump flange is too big you may experience:

  • Your areola could become pulled into the flange and tunnel
  • Painful nipple pinching, pulling, and squeezing
  • Lower breast milk production
  • Your nipple or areola could become white or discolored

When to Size

Throughout pregnancy the breast tissue can be seen going through changes. This includes the size of the breast, as well as the darkening of the areola. Another change would be the size of the nipples. While, for some, the change is subtle, it can still impact the initial fit of the flange. Women tend to retain fluid as the pregnancy progresses, as well as when fluids are administered. The early part of the third trimester or 2-3 weeks postpartum is a great time frame to measure the nipple to get a good idea of what size the nipple will be for the majority of the times needed for pumping. A separate measurement may be needed if pumping and expressing milk is needed immediately postpartum or there are any noticeable changes in size.

Bonus Flange Size Tips

  • If this is your first-time breast pumping, consult with a lactation consultant to assist with determining the flange fit according to nipple shape, areola density, and areola fullness.
  • Measure both of your nipples in case they are different sizes. Some moms need two different flange sizes.
  • Your flange size could change over time, especially after giving birth. Regularly measure your nipples to see if you need to change sizes or not.

Whether a new mom or a veteran, anyone can need help with pumping. An Internationally Board Certified Lactation Consultant (IBCLC) will have extensive training in helping with finding the perfect size flange, along with pumping techniques, storage, feedings, troubleshooting and more!

All content published on the Motif Medical site is credited for information purposes only. This information should not substitute as medical advice, diagnosis, or treatment. Always consult your doctor or qualified health professional with any questions regarding the health of you or your baby.


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